Skeleton Flashcards
braincase
- region of the skull that immediately surrounds the brain
what forms the braincase in different taxa (2)
- agnatha + chondrichthyes: only chondrocranium
- teleostomi: chondocranium (ventral) + dermatocranium (dorsal)
chrondrichthye jaw composition
splanchnocranium:
- palatoquadrate (upper)
- Meckel’s cartilage (lower)
teleostomi jaw composition
dermatocranium - premaxilla, maxilla splanchnocranium - quadrate (upper) - articular (lower)
feeding mechanisms (4)
- prehension
- durophagy
- mastication
- suction feeding
feeding mechanism: prehension (2)
- use jaws and teeth for grasping and holding prey
- generally swallow prey whole
feeding mechanism: durophagy
- use powerful bite to crush hard food
feeding mechanism: mastication (3)
- many mammals
- jaws and teeth used for chewing food
- rhythmic and repetitive movements of the jaw to grind food
suction feeding (2)
- aquatic vertebrae
- rapid expansion of the buccal cavity and pharynx generates sudden decrease in pressure that sucks prey into the mouth
akinetic skull (2)
- skulls with only one mobile joint: the joint between the upper and lower jaws
- only lower jaw is mobile, while upper jaw is immobile relative to the braincase
cranial kinesis (2)
- movement of the upper jaw relative to the braincase
- requires at least one mobile joint between the braincase and the upper jaw
kinetic skull
- skulls with more than one mobile joint
paleostyly
- all pharyngeal arches support the gills
autostyly (2)
- palatoquadrate attached directly and firmly to the braincase
- hyoid arch not involved in jaw suspension
hyostyly (2)
- jaws suspended from the braincase by the hyomandibula, which forms a swinging bridge that allows jaws to protrude (swing forward)
- mobile joint between hyomandibula and braincase, and between hyomandibula and jaws
hyostylic jaw suspension and feeding (2)
- allows for protrusion: pendulum-like swing forward allows the mouth to open wider and close faster
- allows upper and lower jaw to strike prey at same time, gripping prey securely
chondrichthyes: hyoid apparatus (2)
- ventral elements of the hyoid arch
- support the tongue and the floor of the mouth
spiracle (2)
- reduced pharyngeal slit between the hyoid and mandibular arch
- opening for H2O
modified hyostyly (3)
- jaw is attached to the braincase by the hyoid arch, especially the hyomandibula along with several other bones
- several mobile joints, making the jaw extremely kinetic
- mobile joint between upper and lower jaw is between the quadrate and articular
modified hyostyly jaw suspension: feeding mechanism (2)
- catch their prey mainly using suction feeding
- kinetic structure allows for variety of feeding mechanisms: powerful bite
modified hyostyly jaw suspension: mobile joints
mobile joints between:
- maxilla and chondrocranium
- premaxilla and chondrocranium
- maxilla and premaxilla
modified hyostyly jaw suspension: how do the mobile joints affect the jaw (2)
- make upper jaw highly kinetic, allowing for protrusion of the upper jaw
- when lower jaw is depressed, maxilla/premaxilla rotate forward, allowing mouth to open extremely wide
actinopterygii: hyoid apparatus (3)
- formed by ventral elements of the hyoid arch + other arches
- supports tongue and floor of mouth
- forms lateral struts within the floor of the buccal cavity
modified hyostyly jaw suspension: lateral struts of hyoid apparatus (2)
- push lateral walls of buccal cavity outwards when mouth is open
- greatly expands volume of the buccal cavity, generating suction